From f64b9a6af1885cb2b4baf2b4dc299d22a0738965 Mon Sep 17 00:00:00 2001
From: Rahul Ghangas <u6157693@anu.edu.au>
Date: Mon, 11 Jan 2021 12:13:10 +0530
Subject: [PATCH] feat: Add version negotiation handshake wrapper

---
 handshake/negotiate.go | 59 ++++++++++++++++++++++++++++++++++++++++++
 wire/wire.go           |  4 +++
 2 files changed, 63 insertions(+)
 create mode 100644 handshake/negotiate.go

diff --git a/handshake/negotiate.go b/handshake/negotiate.go
new file mode 100644
index 0000000..da956df
--- /dev/null
+++ b/handshake/negotiate.go
@@ -0,0 +1,59 @@
+package handshake
+
+import (
+	"bytes"
+	"fmt"
+	"net"
+
+	"github.com/renproject/aw/codec"
+	"github.com/renproject/aw/wire"
+	"github.com/renproject/id"
+	"github.com/renproject/surge"
+)
+
+const VERSION_BYTES = 2
+type versionType = uint16
+
+func Negotiate(self id.Signatory, h Handshake) Handshake {
+	return func(conn net.Conn, enc codec.Encoder, dec codec.Decoder) (codec.Encoder, codec.Decoder, id.Signatory, error) {
+		e, d, remote, err := h(conn, enc, dec)
+		if err != nil {
+			return nil, nil, remote, fmt.Errorf("handshake before negotiating version: %v", err)
+		}
+
+		var versionBytes [VERSION_BYTES]byte
+		var version versionType
+		cmp := bytes.Compare(self[:], remote[:])
+		if cmp < 0 {
+			if _, err := dec(conn, versionBytes[:]); err != nil {
+				return nil, nil, remote, fmt.Errorf("decoding version: %v", err)
+			}
+			if _, _, err := surge.UnmarshalU16(&version, versionBytes[:], len(versionBytes)); err != nil {
+				return nil, nil, remote, fmt.Errorf("unmarshaling version: %v", err)
+			}
+			if _, err := enc(conn, versionBytes[:]); err != nil {
+				return nil, nil, remote, fmt.Errorf("encoding current version: %v", err)
+			}
+			if version == wire.CurrentVersion {
+				return e, d, remote, nil
+			}
+			return nil, nil, remote, fmt.Errorf("not current version: %v", err)
+		}
+		if _, _, err := surge.MarshalU16(wire.CurrentVersion, versionBytes[:], len(versionBytes)); err != nil {
+			return nil, nil, remote, fmt.Errorf("marshaling current version: %v", err)
+		}
+		if _, err := enc(conn, versionBytes[:]); err != nil {
+			return nil, nil, remote, fmt.Errorf("encoding version: %v", err)
+		}
+		if _, err := dec(conn, versionBytes[:]); err != nil {
+			return nil, nil, remote, fmt.Errorf("decoding version: %v", err)
+		}
+		if _, _, err := surge.UnmarshalU16(&version, versionBytes[:], len(versionBytes)); err != nil {
+			return nil, nil, remote, fmt.Errorf("unmarshaling version: %v", err)
+		}
+		if version == wire.CurrentVersion {
+			return e, d, remote, nil
+		}
+		return nil, nil, remote, fmt.Errorf("not current version: %v", err)
+	}
+}
diff --git a/wire/wire.go b/wire/wire.go
index d76ae38..02b2465 100644
--- a/wire/wire.go
+++ b/wire/wire.go
@@ -11,8 +11,12 @@ import (
 // Enumerate all valid MsgVersion values.
 const (
 	MsgVersion1 = uint16(1)
+	CurrentVersion = MsgVersion1
 )
 
+var romanNumeralDict = map[uint16]struct{}{
+}
+
 // Enumerate all valid MsgType values.
 const (
 	MsgTypePush = uint16(1)